1. Field of Invention
This invention relates to the field of instruments for machine tool setup and calibration.
2. Prior Art
A common task facing a machinist is the alignment of a cutting tool with the workpiece. A number of tools have been developed to aid in this task. They range from simple rulers to precision instruments such as dial indicators and center scopes.
One useful tool used with milling machines is the edge finder as described by Cole et al in U.S. Pat. No. 1,984,864. This is a simple tool that is mounted in the quill and slowly brought into contact with the edge of the workpiece while the spindle is rotating. The spring loaded end of the edge finder will indicate when the edge is in alignment with the quill.
Another useful tool is the coaxial indicator. This is used to align the quill over the center of an existing hole. It is a specialized dial indicator that mounts in the quill and has a long feeler arm. As the spindle is rotated by hand the feeler arm rotates around the inner surface of the hole and will show any misalignment.
A centerscope is a specialized type of microscope had been adapted for machine tool use. It uses similar optics to a microscope but has a mirror in the optical path allowing the body to have a bend. The objective lens is vertical, in line with the quill axis, but the eyepiece is off to the side at an angle. This arrangement allows the machinist to see where the quill center line intersects with the surface of the workpiece. When the centerscope is removed from the quill and the cutting tool mounted, the cutting tool will be exactly aligned with the workpiece.
3.Objects and Advantages
Most of the current alignment methods require that the tool be removed from the spindle. This is time consuming and disruptive of work flow. Some of these methods only work for edges and not for scribed lines. They all require that the machine be shut down. All of these devices require the machine operator to work in close proximity to the spindle thereby increasing the risk of injury.
The present invention solves the problem with other alignment methods.
The advantages to the present invention are;                (a) Does not need to be removed while machine is operating.        (b) Magnifies the image of the workpiece resulting in better alignment.        (c) No moving parts.        (d) Safer, can be used remotely.        (e) Changing tools does not affect the calibration.        (f) Easily removed.        (g) Easily calibrated.        
The invention combines these features in a way that provides significant advantages over other means of machine tool alignment.